In designing polyphonic synthesisers an important balance must be struck between price and specification, with particular reference to the number of simultaneous notes available. The Teisco SX400 and Yamaha CS50 boast a large number of performance features including keyboard touch-sensitivity but are limited to four notes at a time; the Jupiter 8 or Polymoog offer more notes but at a much greater price. Two recent polysynths, the Korg Polysix and the Roland Juno 6, have attempted to establish a new standard, a six-note synth with a single oscillator assigned to each note, and it is refreshing to see that the trade-off of specification against price has for once worked well.

The major differences between these two synths is the Juno's lack of programmability, which enables it to be sold for some £500 cheaper than the Korg at about £700. Rather than producing a scaled-down version of their Jupiter 8, Roland have chosen to expand their popular SH09 monosynth into a polyphonic version, and the finished product boasts a five-octave keyboard and highly stable digital versions of the SH09's oscillators - no tuning problems here! Operation is extremely simple, the six DCOs (digitally controlled oscillators), VCFs and VCAs being controlled by common sliders, and a built-in chorus and arpeggiator provide a selection of unusual effects.

The oscillators offer triangle, square and pulse width modulation options, together with sub-octaves which thicken up the sound considerably. A high pass filter makes creation of thin reedy textures possible, while the single ADSR envelope shaper assigned to the VCAs and/or VCFs gives the usual range of sound shapes and effects. Particularly impressive is a slow attack and sharper decay used on notes picked from all over the keyboard, since each note has its own VCF and VCA. A horizontal sprung lever on the left of the keyboard can be used to control the oscillators and/or filters to any desired amount, giving a maximum possible pitch bend of around a fifth, and nearby there is a white button which introduces modulation for as long as it is held down, as an alternative to the delay modulation, also available. The chorus on the extreme right provides two fixed chorus modes already familiar from the RS09 strings and SH09 hybrid keyboard. This section certainly does a lot to improve the texture, particularly of string sounds, and the combined effect of chorus, sub-octave pulse width modulation and vibrato is quite stunning!

The remaining major feature is the arpeggiator which plays in series up, down or up and down the keyboard any notes which are held down, at any speed. The arpeggiator can be latched so that it plays with "hands-off", and can be driven from an external clock such as a rhythm box, the arpeggio changing as soon as a new set of notes is touched. The top and bottom notes are always played twice in "up/down" mode, yet it is still possible to create a wide range of sequencer-like patterns.

Circuit Features

The heart of this synthesiser is an 8049 8-bit microprocessor, running at 1MHz. It has a 2K ROM area which has been programmed by Roland's software engineers. The device accesses keyboard data representing the keys pressed (up to six at once) via input Port 1 and this is outputted as multiplexed 8-bit data for conversion to a key control voltage (through a ladder resistor network) and gate pulse (through a 4099 8-bit addressable latch). Four 4051 8-channel analogue de-multiplexer/multiplexers are controlled by Port 2 of the 8049 and synchronise the DCOs with pulse wave and sawtooth waveforms, and also the VCF. Both VCF and VCA have ADSR control from a dedicated device, IR3R01. All this circuitry is on one large CPU board located in the instrument base (see photos). Next to it is the power supply (+5, +15, -15V). The performance controls have their electronics directly underneath. The neat layout is completed by two main control front panel boards which send control information to the CPU board. White noise is generated by an amplified selected transistor (2SC945) while Arpeggio (modes, range) and Key Transpose are operated by setting the initial data lines into Port 1. A rear jack panel gives screwdriver adjustment Tuning (±50 cents), pedal Hold of keys played (a make/break pedal such as Roland DP-2), external VCF cut-off control (using a Roland FV-200 pedal), stereo phone socket (8-200 ohms) and mono or stereo (the latter really essential for best results), switched for -30dB, -15dB and 0dB.

There is also an external socket for control of Arpeggio rate which is a useful feature (one step per pulse over +2.5V). Any problems in finding a suitable control trigger can be overcome with this month's trigger project - the E&MM Synclock in particular gives rhythmic variety and, if selected to give a three pulse sequence length (running at a fast rate from a separate slow oscillator) will play three note chords. The Arpeggio mode can be up, up and down or down over a range of 1, 2 or 3 octaves, with internal clock rate variable from 1.5Hz to 50Hz.

A standard keyboard of 61 keys covering 5 octaves can be switched up one or two octaves. DCO pulse width modulation is effective from 50 to 97 per cent and LFO modulation of the oscillators is a maximum 300 cents. Filters in the Juno, as with most Roland equipment, are very smooth in operation, with versatile control of the low pass VCF as it goes into oscillation with Resonance increased. The Cut-off frequency of the LPF covers 4Hz-40kHz and envelope modulation covers the normal 10 octaves (whilst LFO modulation covers 6 octaves).

The keyboard control voltage follower will open the LPF from 0-100 per cent for precise tonal shaping over the whole keyboard range.

A 'gate' keying option on the VCA adds a quick change of organ style touch to the standard ADSR controls. The latter can be set for Attack (1mS - 3S), Decay (2mS - 10S), Sustain (0-100 percent) and Release (2mS - 10S). The extremely short time settings give the Juno great clarity for percussive effects and, in conjunction with filter control, can produce dramatic harmonic changes. The maximum settings are acceptable, although special effects need longer times but are necessarily limited to feasible control pot spread.

LFO rate is from 3 cycles every second to 20Hz and delay is adjustable from 0 to 214 seconds.

The control section to the left of the keyboard offers volume and octave transpose setting plus slider adjustment of DCO and VCF bend sensitivity via a left/right spring-loaded lever. The DCO control is limited to ± fifth interval. Octave jumps here are always preferable as maximum parameters but not easily achieved. A novel addition (reminiscent of the early EMS synthesisers) is an LFO trigger button that provides manual control rather than continuous vibrato etc.

The Key Transpose is an interesting feature for musicians who want to play in a variety of keys but find the task difficult! By pressing any note on the keyboard (except C, which brings you back home again), a touch of the Key Transpose button will put the keyboard white note scale in your new key selected. Of course, you will have to turn the volume down while you do the setting on stage! The top octaves have limited transposition and its main use may be for playing from scores with orchestral transposing instruments. Nevertheless, the circuitry is all there and this control is provided via a single contact switch to two Port 1 input lines.

The Chorus effect is fast becoming a permanent feature on polyphonic synthesisers and Roland were probably the first to put it there. Three speed control of the ensemble rate is possible by switching in or out two push buttons, giving slow rates of 0.4Hz and 0.6Hz plus (together) a faster 8Hz tremolo chorus effect. The chorus is based around two identical circuits incorporating two ICs (MN3009 and MN3101).

The instrument is superbly finished, with veneered wood end pieces and logically laid out black metal control panels in a very slim case measuring 1060(W) x 113(H) x 378(D) mm and weighing 11kg.

The first impression of the Juno 6 is that it simply doesn't have many knobs on it, but it soon becomes clear that this keyboard can produce all the standard polysynth sounds and more, including strings, organ and a very respectable lead synth. The overall sound is crisp, clear and powerful, with a very smooth filter, and the price is reasonable. What more could anybody ask?

The Roland Juno 6 retails at £699 inc. VAT and is distributed in the UK by Roland (UK) Ltd, (Contact Details).